RTCPeerConnection.addTrack should return sender

[shannah]

RTCPeerConnection.addTrack. should return the RTCRtpSender.

Currently I need to work around it with this:

var sender = conn.addTrack(track, stream);
if (!sender) {
    sender = conn.getSenders().find(function(s){return s.track===track;});
}

[hthetiot]

@shannah thank you, should be fixed by #572 see Testing instruction.

[hthetiot]

Feel free to comment if that does not fix it, i will re-open.
Notice this a SHAM not a SHIM, I may manage RTCRtpSender instances later on version 8+